Texture structure manufacturing method

ABSTRACT

Provided is a texture structure manufacturing method with which a texture structure can be obtained simply. The texture structure manufacturing method comprises: growing a layer including a randomly distributed nanostructure on a major surface of a base material; forming a light-scattering body having the nanostructure embedded therein; and exposing a surface of the light-scattering body by removing a part or all of the base material and the layer including the nanostructure.

TECHNICAL FIELD

The present invention relates to a texture structure manufacturingmethod.

BACKGROUND ART

In an optical device such as a photoelectric conversion element and anoptical sensor, a concave and convex structure for reducing lightreflection may be formed on a light receiving surface.

In a solar battery described in Patent Literature 1 (PTL1), a moth eyestructure is formed by a conductive substance on a transparentconductive layer having a texture structure.

An imaging element described in Patent Literature 2 (PTL2) includes aphotoelectric conversion portion for converting received light intoelectric charges, and a semiconductor substrate including thephotoelectric conversion portion, in which a large number of regionshaving a refractive index being different from a refractive index of thesemiconductor substrate are formed between a surface of thesemiconductor substrate where light is incident, and the photoelectricconversion portion. The region is formed to have a shape such that anarea is large at a depth close to the surface of the semiconductorsubstrate where light is incident, and an area is small at a depth farfrom the surface.

In a solid-state imaging device described in Patent Literature 3 (PTL3),a semiconductor substrate is engraved by dry etching according to aresist pattern, and a concave portion having a V shape in cross-sectionis formed.

CITATION LIST Patent Literature

[PTL1] Japanese Patent Application Laid-Open No. 2013-179217

[PTL2] Japanese Patent Application Laid-Open No. 2015-18906

[PTL3] Japanese Patent Application Laid-Open No. 2015-220313

SUMMARY OF INVENTION Technical Problem

For example, when an optical image sensor employing a compoundsemiconductor having a random light scattering surface is manufactured,it is desirable to form the scattering surface at a position as close aspossible to a light receiving layer, for the purpose of reducingcrosstalk by scattered light.

Further, it is often the case that an optical image sensor employing acompound semiconductor has a structure formed by bonding, by using aflip chip bonding, a chip including a light receiving portion, and areadout circuit chip by a silicon complementary metal oxidesemiconductor (Si-CMOS). At this occasion, a scattering surface isformed on a back surface of the light receiving portion. Therefore, whena scattering surface is formed before flip chip bonding, the flip chipbonding becomes difficult, since the chip having the light receivingportion is very thin, and has a microstructure.

Further, when thinning is performed from a back surface up to a positionnear a light receiving layer after flip chip bonding, and thereafter, arandom pattern for forming a scattering surface is formed byphotolithography or the like, it is difficult to satisfy both ofproductivity and reliability.

An object of the present invention is to solve the above-describedproblems, and provide a texture structure manufacturing method capableof acquiring a texture structure in a simplified way.

Solution to Problem

To achieve the above-mentioned object, a method for manufacturing atexture structure according to the present invention, comprises: growinga layer including a randomly distributed nanostructure on one majorsurface of a base material; forming a light-scattering body having thenanostructure embedded therein; and exposing a surface of thelight-scattering body by removing a part or whole of the base materialand the layer including the nanostructure.

Advantageous Effects of Invention

The present invention is able to provide a more simplified manufacturingmethod of an optical device having a texture structure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating one exampleof a thin film semiconductor optical sensor to be manufactured by atexture structure manufacturing method according to an exampleembodiment of the present invention.

FIG. 2(a) is a first schematic diagram illustrating a principle of theoptical sensor according to the example embodiment, and FIG. 2(b) is asecond schematic diagram illustrating the principle of the opticalsensor according to the example embodiment.

FIGS. 3(a) to 3(d) are process diagrams illustrating a random texturestructure manufacturing method according to a background art.

FIG. 4 is a cross-sectional view of a semiconductor optical device to bemanufactured by a texture structure manufacturing method according to afirst example embodiment of the present invention.

FIGS. 5(a) to 5(f) are cross-sectional views illustrating amanufacturing process of the semiconductor optical device in FIG. 4.

FIGS. 6(a) to 6(d) are cross-sectional views illustrating themanufacturing process of the semiconductor optical device in FIG. 4.

FIG. 7 is a graph illustrating a relationship between a quantum dotgrowth rate and a quantum dot surface density.

FIG. 8 is an atomic force microphotograph of a manufacturing example oflow-density quantum dots.

FIG. 9 is a surface photograph of a manufactured random texturestructure.

FIG. 10 is a cross-sectional view of a semiconductor optical device tobe manufactured by a texture structure manufacturing method according toa second example embodiment of the present invention.

FIGS. 11(a) to 11(d) are cross-sectional views illustrating amanufacturing process of the semiconductor optical device in FIG. 10.

FIGS. 12(a) to 12(d) are cross-sectional views illustrating themanufacturing process of the semiconductor optical device in FIG. 10.

FIG. 13 is an atomic force microphotograph of a manufacturing example ofa nanostructure having a structure in which a plurality of quantum dotsare aggregated.

FIG. 14 is an electron microphotograph of a manufacturing example of ananostructure formed by combining a large number of quantum dots.

FIG. 15 is a cross-sectional view of a semiconductor optical device tobe manufactured by a texture structure manufacturing method according toa third example embodiment of the present invention.

FIGS. 16(a) to 16(d) are cross-sectional views illustrating amanufacturing process of the semiconductor optical device in FIG. 15.

FIGS. 17(a) to 17(d) are cross-sectional views illustrating themanufacturing process of the semiconductor optical device in FIG. 15.

FIG. 18 is a cross-sectional view of a thin film semiconductor opticalsensor to be manufactured by applying a texture structure manufacturingmethod according to a fourth example embodiment of the presentinvention.

FIGS. 19(a) to 19(d) are cross-sectional views illustrating amanufacturing process of the thin film semiconductor optical sensor inFIG. 18.

FIGS. 20(a) to 20(d) are cross-sectional views illustrating themanufacturing process of the thin film semiconductor optical sensor inFIG. 18.

FIG. 21 is a cross-sectional view of a thin film semiconductor opticalsensor to be manufactured by applying a texture structure manufacturingmethod according to a fifth example embodiment of the present invention.

FIGS. 22(a) to 22(d) are cross-sectional views illustrating amanufacturing process of the thin film semiconductor optical sensor inFIG. 21.

FIGS. 23(a) to 23(c) are cross-sectional views illustrating themanufacturing process of the thin film semiconductor optical sensor inFIG. 21.

FIGS. 24(a) and 24(b) are cross-sectional views illustrating themanufacturing process of the thin film semiconductor optical sensor inFIG. 21.

EXAMPLE EMBODIMENT

Preferred example embodiments according to the present invention aredescribed in detail with reference to the drawings.

Before a specific example embodiment according to the present inventionis described, an overview of the present invention is described. FIG. 1is a cross-sectional view schematically illustrating one example of athin film semiconductor optical sensor to be manufactured by applying atexture structure manufacturing method according to an exampleembodiment. An optical image sensor 1 according to the present exampleembodiment has a structure in which a first electrode 8, a substrate 2,a light reflecting body 6, a light absorbing medium 3, and a secondelectrode 7 are laminated. Incident light 9 is incident on a surface ofthe light absorbing medium 3 of the optical image sensor 1. Note thatthe following description is made based on a premise that a direction inwhich the first electrode 8 of the optical image sensor 1 is present isa down direction, and a direction in which the second electrode 7 ispresent is an up direction. Description on up and down directions in thefollowing description does not limit a direction in which the opticalimage sensor 1 is disposed.

The first electrode 8 is formed in contact with the substrate 2. Thesecond electrode 7 is formed in contact with the light absorbing medium3. By applying an appropriate bias voltage to the first electrode 8 andthe second electrode 7, it is possible to withdraw a photocarriergenerated by light absorption. Further, although it depends on a devicestructure, a bias voltage to be applied between the first electrode 8and the second electrode 7 is generally about several volts.

A GaAs or the like may be used for the substrate 2. It is possible toemploy an n-type semiconductor substrate in which an Si of about 1 to3×10¹⁸ cm⁻³ is doped in a GaAs.

The light reflecting body 6 is laminated on the substrate 2. The lightreflecting body 6 is in contact with a surface of the substrate 2 on aside opposite to a surface to be connected to the first electrode 8. Thelight reflecting body 6 is able to be made of a metal or the like. Thelight reflecting body 6 reflects light transmitted through the lightabsorbing medium 3 toward the light absorbing medium 3. The lightreflecting body 6 acts to reflect light that is not totally reflected ona back surface texture structure 5 in such a way that the light does notescape toward the substrate 2 side, and return the light to the lightabsorbing medium 3 again.

The light absorbing medium 3 is laminated on the light reflecting body6. As the light absorbing medium 3, a material having a refractive indexbeing capable of absorbing light having a center wavelength λ to bedetected by the optical image sensor 1 is used. A thickness of the lightabsorbing medium 3 is sufficiently smaller than a light penetrationlength (inverse number of an absorption coefficient). The lightabsorbing medium 3 has a light incident surface texture structure 4having concaves and convexes on a surface where the incident light 9 isincident. The light absorbing medium 3 also has the back surface texturestructure 5 on an interface with respect to the light reflecting body 6.A typical structure scale of the back surface texture structure 5 is d.When the light incident surface texture structure 4 and the back surfacetexture structure 5 are formed, light reciprocates multiple times withinthe light absorbing medium 3 by total reflection of light on aninterface of the light absorbing medium 3. On the other hand, there islight that is not totally reflected on the light absorbing medium 3, andescapes toward the substrate 2 transmitted through the light absorbingmedium 3. Light that has transmitted through the light absorbing medium3 is reflected on the light reflecting body 6, and is incident on thelight absorbing medium 3 again. A typical structure scale means anaverage pitch (period) of concave and convex. Note that a texturestructure in the present description means both of a structure havingconcaves and convexes on an exposed surface of a substance, and astructure having concaves and convexes on a laminated interface of thesubstance with respect to another substance.

Light transmission and light reflection on individual surfaces havingconcaves and convexes constituting the light incident surface texturestructure 4 and the back surface texture structure 5 locally depend on aplanar direction thereof, and follows a Snell's law. However, sinceorientations of individual surfaces having concaves and convexes areirregular, the light incident surface texture structure 4 and the backsurface texture structure 5 function, as a whole, as a light scatteringsurface on which light reflection isotropically occurs on a hemispheresurface. Because of necessity that light reflection on individualsurfaces depend on a planar orientation, the typical structure scale dof the light incident surface texture structure 4 and the back surfacetexture structure 5 is required to satisfy d>(λ/n), by referring to thecenter wavelength λ and a refractive index n of the light absorbingmedium 3. In order to verify whether d>(λ/n) is satisfied, it may besufficient to evaluate an average pitch of concave and convex of anysample region by various types of surface roughness measuring devices.Note that a depth of a concave and a height of a convex of both thelight incident surface texture structure 4 and the back surface texturestructure 5 are equal to about the center wavelength λ.

In a thin film semiconductor optical sensor as one example of theoptical image sensor according to the present example embodiment, bothof multi-path light absorption enhancement by a light trap effect, andsemiconductor surface antireflection by a moth eye effect are achievedin a desired wavelength band by applying a single texture structure to alight incident surface. In a thin film semiconductor optical sensor asone example of the optical image sensor according to the present exampleembodiment, both of multi-path light absorption enhancement by a lighttrap effect, and semiconductor surface antireflection by a moth eyeeffect are achieved in a desired wavelength band without causing aproblem on reliability and productivity. In the following, details aredescribed.

First, multi-path light absorption enhancement by a light trap effect isdescribed. It is conventionally known that light can be efficientlytrapped by effectively utilizing total reflection within an opticallythin medium having a higher refractive index than air being an externalenvironment. As expressed by the Fresnel equations, total reflectionwithin a medium occurs only for light having a large incident angle (asmall angle with respect to an interface). Light other than the above istransmitted and radiated into the air by refraction on an internalinterface. A light mode in which light is incident from the air into amedium, and a light mode in which light is radiated from the inside of amedium into the air, which is an inverse mode of the former light modehave a one-to-one correspondence. When this is referred to as atransmission mode, on a flat interface, the transmission mode does notcombine at all with a total reflection mode in which total reflectionoccurs on an internal interface of a medium. Therefore, when light isincident from the air into a thin film absorbing medium having a flatinterface, only double-path light absorption in which light reciprocatesone time occurs.

In order to achieve multi-path light absorption, a means for combining atransmission mode with a total reflection mode is necessary. Texturingan interface is one of effective combining means for combining atransmission mode with a total reflection mode. When light scatteringreflection on a textured interface occur isotropically on a hemispheresurface, a probability with which light subjected to total reflection ona textured surface is transmitted through the air without totalreflection on a succeeding textured surface is decreased to 1/n².Consequently, light is trapped in an optically and sufficiently thinuniform medium having a refractive index n, which is surrounded by atextured surface, and emitted to the air after undergoing totalreflection on an interface n² times in average. As a result that a pathlength until light is emitted to the air is multiplied n² times, a lightintensity within the medium is enhanced n² times, and absorptionefficiency of the medium improves. Absorption enhancement occurs bymulti-path light absorption.

In order to enhance absorption by trapping light, the following twoconditions are necessary.

(1) A medium has a high refractive index, and is optically thin, and

(2) Light scattering reflection isotropically occur on a hemispheresurface at a textured interface in order to effectively combine atransmission mode and a total reflection mode.

In order to satisfy the condition (2), it is necessary that a typicalstructure scale of a texture structure is larger than a wavelength orderof incident light, in view of necessity that the textured surface has astructure in which a planar direction is random, and light reflection onindividual surfaces of the texture structure depends on individualplanar orientations.

Next, surface antireflection by a moth eye effect is described. In atextured surface having a structure that changes at a scale smaller thana wavelength order of incident light, a moth eye effect such that avertical reflectance of air with respect to a medium on a mediuminterface having a refractive index n ideally decreases from((n−1)/(n+1))² to 0 is known. This is because, in a texture structurehaving a typical structure scale smaller than a wavelength order, anoperation on incident light by a diffraction effect does not depend on aplanar orientation of individual concave or convex, and functions as onekind of a refractive index matching layer in which an effectiverefractive index gradually changes from 1 to n. Although a moth eyeeffect functions as a refractive index matching layer in which a drasticchange of an interface refractive index is buffered irrespective of anoptical thickness of a medium, the moth eye effect does not contributeat all to combining a transmission mode and a total reflection mode.Since a decrease in reflectance increases an amount of light thatreaches an absorbing layer, absorption enhancement occurs.

As described above, in an aspect of light absorption enhancement, in anoptically thin medium having a typical structure scale of a texturestructure larger than a wavelength of light, multi-path light absorptionenhancement by a light trap effect is important. When the typicalstructure scale of the texture structure is small, incident surfaceantireflection by a moth eye effect is important irrespective of anoptical thickness of a medium. In other words, in a textured surfacehaving concaves and convexes arranged at a single pitch, a light trapeffect is important for light having a wavelength shorter than astructure scale of the textured surface, and a moth eye effect isimportant for light in a long wavelength region. Since these conditionsare obviously exclusive of each other, it has been believed that, in atexture structure having concaves and convexes at a single pitch, it isnot possible to simultaneously receive benefits of a light trap effectand a moth eye effect for the purpose of absorption enhancement.

For example, in a case of a silicon solar battery, since energyacquisition is a purpose, there is a demand for increasing photoelectricconversion efficiency of light in a broad wavelength region from a nearinfrared to an ultraviolet region. In order to enhance light absorptionin a wavelength region longer than an optically thin bandgap (to 1 μm)by surface texturing, a random textured surface having a structure scalelarger than 1 μm where a light trap effect becomes valid is necessary.In order to enhance light absorption in an optically thick ultravioletregion of a wavelength 300 nm or shorter by surface antireflection, aconcave and convex structure of a scale smaller than 300 nm at which amoth eye effect becomes valid is necessary. Therefore, it has beendifficult to enhance incident light absorption of a silicon solarbattery in a wide wavelength region by a texture structure havingconcaves and convexes at a single pitch.

By forming, on a surface, a double layered texture structure in whichtexture structures are laminated, it may be possible to achieve asilicon solar battery that simultaneously achieves a light trap effectand a moth eye effect, and has a high photoelectric conversionefficiency of light in a wide wavelength region from a near infrared toan ultraviolet region by absorption enhancement. However, in a doublelayered texture structure, superiority is low in terms of productivityand reliability.

On the other hand, in a case of an optical sensor aiming at informationacquisition, unlike a solar battery, the optical sensor may befrequently used for detecting light in a specific narrow wavelengthband. In this case, it becomes possible to achieve a thin filmsemiconductor optical sensor that simultaneously receives benefits of alight trap effect and a moth eye effect, and has a high photoelectricconversion efficiency of light in a target wavelength band by absorptionenhancement. In the following, this is described with reference to thedrawings.

FIG. 2(a) is a first schematic diagram illustrating a principle of anoptical sensor according to the present example embodiment. A case thata texture structure in which a planar orientation is random is presenton a light incident surface and a back surface is considered. FIG. 2(a)illustrates a relationship among a light trap effect, a moth eye effect,and a wavelength of incident light. A horizontal axis d indicates atypical structure scale of a texture structure. When it is assumed thata detection target center wavelength of the optical sensor is k, aneffective light wavelength within a medium having a high refractiveindex (n>1) becomes λ/n (d<λ). When it is assumed that a typicalstructure scale of a texture structure of a front surface and a backsurface is d>λ/n, since light scattering reflection occur when light isreflected on an interface within a medium, light is trapped within anoptically thin absorbing medium for use in a thin film semiconductoroptical sensor.

On the other hand, when it is assumed that d<λ, a moth eye effect occursfor incident light from an outside of the medium. In a case of anoptically thin medium in which a structure scale d of a texturestructure satisfies λ/n<d<λ, when light of the target center wavelengthλ is incident from a vicinity in a vertical direction, the incidentlight in which reflection is decreased by a moth eye effect propagatesin a direction substantially vertical to the medium according to aSnell's law. The propagated light is isotropically scattered andreflected on a hemisphere surface by the texture structure of the backsurface, and is isotropically scattered and reflected on the hemispheresurface again by the texture structure of the front surface afterre-propagation. Each time the propagated light is scattered andreflected, a probability with which the light is not totally reflectedand is transmitted to the outside of the medium is 1/n². Thus, observedlight is trapped within the medium, and is emitted to the air afterrepeating total reflection on a textured surface n² times in average.

FIG. 2(b) is a second schematic diagram illustrating the principle ofthe optical sensor according to the present example embodiment, and is adiagram illustrating, by setting λ on a horizontal axis, an effectoccurred when light of the target center wavelength λ is incident froman outside of an absorbing medium having a refractive index n and inwhich a concave and a convex of a typical structure scale d is formed.The diagram illustrates that both of reduction of incident lightreflectance by a moth eye effect, and multi-path light absorption bylight traping are achieved for a light wavelength region where d<λ<nd. Avalue for a semiconductor material is from n to about 3.5 from anatom-filling density. Therefore, a wavelength bandwidth that can achieveboth of the two effects approximately becomes Δλ=(n−1)d to 2.5d. When acenter of the band (n+1)d/2 is made coincide (λ=(n+1)d/2) with thecenter wavelength λ of observation target light, Δλ becomesΔλ=2λ(n−1)/(n+1). When it is assumed that n=3.5, the value becomes avalue of an order of a center wavelength of detection target light,namely, Δλ to 1.11λ. Therefore, when this principle is applied todetection of light in an infrared region where λ>1 μm, it becomespossible to achieve a thin film semiconductor optical sensor thatsimultaneously receives benefits of a light trap effect and a moth eyeeffect of detection target light in a substantially and practicallysufficient band, and has a high photoelectric conversion efficiency byabsorption enhancement due to each of the effects.

By using the above-described principle, the optical sensor according tothe present example embodiment achieves a thin film semiconductoroptical sensor that simultaneously receives benefits of a light trapeffect and a moth eye effect for light in a target wavelength band by asingle pitch structure, and has a high photoelectric conversionefficiency by absorption enhancement, based on each of the effects. Inview of this, a texture structure in which a planar direction is randomis formed on a light incident surface and a back surface of a lightabsorbing medium, and the typical structure scale d of the texturestructure becomes to satisfy (λ/n)<d<λ according to the centerwavelength λ of target light. Further, a midpoint (n+1)d/2 between thestructure scale d viewed from the outside of the medium, and a typicalstructure scale nd viewed from the inside of the medium is made coincidewith the center wavelength λ of target detection light. In other words,λ=(n+1)d/2 is satisfied. When it is assumed that λ=1 μm and n=3.5,(λ/n)<d<λ is 0.28 μm<d<1 μm. When it is assumed that λ and d satisfyλ=(n+1)d/2, d=0.44 μm.

Conventionally, a photolithography method is employed for forming arandom texture structure in which at least either a pitch of concave andconvex, or an individual planar direction of a concave and a convex isirregular. In other words, a general method includes growing asemiconductor layer on a light absorbing layer of an optical sensor,forming a mask having a random pattern on a flat surface of thesemiconductor layer, and manufacturing by a chemical etching method.

FIGS. 3(a) to 3(d) illustrate an etching method to be specificallyperformed. As a mask for a random pattern, for example, a randomcircular opening pattern as illustrated in a plan view of FIG. 3(a) isprepared. Gray portions in FIG. 3(a) indicate random openings. A maskfor a random pattern is formed on a surface of a semiconductor layer inwhich a light absorbing medium and the like are formed. FIG. 3(b)illustrates a cross-sectional view of representative large and small twoopenings among random circular opening patterns. A light absorbingmedium having a mask formed as described above is immersed in an etchantfor an appropriate time. The appropriate time is a time to be determineddepending on a size, an interval, and the like of a random pattern,which is intended to be manufactured, as far as each of patterns are notuniform. Thus, a small opening portion is etched into a small hole, anda large opening portion is etched into a larger hole. Consequently, arandom structure having a shape as illustrated in the cross-sectionalview of FIG. 3(c) is formed.

FIG. 3(c) illustrates a case after isotropic etching, and illustrates acase (moistening speed into a substrate)>(side etching speed of aportion beneath a mask (end portion)). In this example, an isotropicetchant (e.g. a solution in which a small amount of Br is dissolved inmethanol) is used. FIG. 3(d) illustrates a case after anisotropicetching. When etching is performed by using an anisotropic etchant(e.g., a mixed solution of ammonia water and hydrogen peroxide water),while using a mask pattern having square (or polygonal) random openings,a random structure composed of inverted pyramidal holes as illustratedin the cross-sectional view of FIG. 3(d) is formed.

However, when a texture structure is manufactured by the present method,it is necessary to manufacture a mask for a random pattern. The randompattern is required to be such that a size distribution and a spacedistribution of openings are random with respect to a predeterminedwavelength. Designing a mask for the random pattern is cumbersome.Further, since a photolithography method is employed, it is necessary toperform a process of forming a random pattern on a resist film, adielectric film, or the like, performing etching by using the formedrandom patterns as a mask, and then removing the resist film or thedielectric film. Therefore, a wafer may be contaminated accompanied bythe process of removing the resist film or the dielectric film.

Further, generally, a random texture structure exhibits the effects moreeffectively by forming the random texture structure on a light absorbinglayer, a light emitting layer, and the like on a substrate side, or bothof the substrate side and a wafer surface side, which is opposite to thesubstrate side.

When a random texture structure is manufactured by a photolithographymethod, it is easy to manufacture the random texture structure on awafer surface side (side opposite to a substrate side). However, when arandom texture structure is tried to be manufactured on the substrateside being opposite to the wafer surface side, it is necessary to removea semiconductor substrate of a certain thickness over the entire surfaceor partially. When a semiconductor substrate is removed over the entiresurface, handling may become difficult due to thinning of a wafer.Further, when a semiconductor substrate is partially removed, it isnecessary to manufacture a hole structure (barus structure) in which asemiconductor substrate is removed except for a region where lightemission/light reception is performed, and manufacture a random texturestructure on a bottom portion of the hole. Therefore, there occurs aproblem such that a resist film cannot be uniformly coated, contactexposure cannot be performed, or the like. There is an issue that aprocess becomes extremely difficult by an ordinary photolithographymethod.

First Example Embodiment

A texture structure manufacturing method according to a first exampleembodiment of the present invention, and an optical image sensor as oneexample of a device to be manufactured by the manufacturing method andan operation principle thereof are described. More specifically, as oneexample of the optical image sensor, a thin film semiconductor opticalsensor is described. FIG. 4 is a cross-sectional view of a semiconductoroptical device to be manufactured by the texture structure manufacturingmethod according to the first example embodiment of the presentinvention. FIGS. 5(a) to 5(f), and 6(a) to 6(d) are cross-sectionalviews illustrating a manufacturing process of the semiconductor opticaldevice in FIG. 4.

(Description on Configuration)

The semiconductor optical device in FIG. 4 includes a semiconductorsubstrate 11, a first semiconductor layer 12, a second semiconductorlayer 13, a third semiconductor layer 14, a semiconductor active layer15, and a semiconductor cover layer 16. In particular, the semiconductoroptical device in FIG. 4 is a semiconductor optical device having arandom texture structure 20 within a barus structure.

(Description on Manufacturing Method)

Referring to FIGS. 4 to 6, a texture structure manufacturing methodaccording to the present example embodiment, and a semiconductor opticaldevice manufacturing method according to the present example embodimentare described. The present example embodiment is described based on apremise that GaAs is used for the semiconductor substrate 11, the firstsemiconductor layer 12, and the third semiconductor layer 14. Further,the present example embodiment is described based on a premise that aquantum dot layer made of InAs is used as the second semiconductor layer13 and the semiconductor cover layer 16.

Furthermore, the present example embodiment is described based on apremise that a light absorbing layer in an infrared region constitutedof a plurality of semiconductor layers including InAs quantum dots isused as the semiconductor active layer 15.

Note that the present example embodiment is merely one example of thepresent invention, and may be modified as far as the modificationexhibits an advantageous effect described in the present exampleembodiment by a component factor and the like of a device structure. Thesemiconductor material may be another material, and the nanostructuremay be another structure. Further, a case that a molecular beam epitaxymethod is employed for manufacturing a semiconductor laminate structureis described. However, another method such as an organic metal thermaldecomposition method may be employed.

First, the semiconductor substrate 11 made of GaAs is prepared, andintroduced into a growing device. In the present process, a molecularbeam epitaxy device is employed as one example of the growing device.After a natural oxide film on a substrate surface is removed by anordinary substrate surface cleaning treatment such as raising asubstrate temperature up to about 600° C., while radiating As, the firstsemiconductor layer 12 made of GaAs is grown on one major surface of thesemiconductor substrate 11 (FIG. 5(a)). The first semiconductor layer 12is a buffer layer. As far as a surface of the semiconductor substrate 11has crystallinity and cleanliness sufficient for succeeding growth, thefirst semiconductor layer 12 may be omitted. In the followingmanufacturing method, unless otherwise specifically mentioned, it isassumed that a manufacturing process in a state of a wafer for asemiconductor optical image sensor is described.

Next, the second semiconductor layer 13 is grown, as one example of alayer having a concave and convex surface on which nanostructures arerandomly distributed (FIG. 5(b)). The present example embodimentdescribes an example in which a quantum dot made of InAs is used as ananostructure. Specifically, the second semiconductor layer 13 made ofInAs quantum dots is grown by supplying In by an amount equivalent to1.8 molecular layer (ML) at a substrate temperature of 480° C. in an Asatmosphere. Since there is a lattice constant difference of about 7.2%between GaAs and InAs, the grown InAs grows into a three-dimensionalisland shape. The growth of the three-dimensional island shape isreferred to as a Stranski Krastanov (SK) mode growth. Such thethree-dimensional islands (quantum dots) made of InAs are formed at arandom position on a growing surface, and has a characteristic such thata very thin (equivalent to about 1 to 2 molecular layers)In_(x)Ga_(1-x)As or InAs two-dimensional layer accompanies. Further, itis possible to control a forming surface density of InAs quantum dots bychanging a growing parameter. For example, when a growth rate of InAsquantum dots is decreased, the density decreases, and when the growthrate is increased, the density increases. In other words, it is possibleto control an average distance between quantum dots, according to anoperating wavelength of a semiconductor active layer.

FIG. 7 is a graph illustrating a relationship between a quantum dotgrowth rate and a quantum dot surface density. FIG. 7 illustrates oneexample of a relationship between a growth rate of InAs quantum dots anda surface density. By changing a supply rate of InAs from 0.01 ML/s to0.2 ML/s, it is possible to control a forming density of InAs quantumdots from 1×10⁸ cm⁻² to 2×10¹⁰ cm⁻². FIG. 8 illustrates an atomic forcemicrophotograph of InAs quantum dots, when a forming density of InAsquantum dots is set to 1×10⁹ cm⁻² by controlling a growth rate. In thiscase, an average interval of quantum dots becomes about 0.33 μm fromcalculation of a forming density. In other words, when it is assumedthat a refractive index of a semiconductor is 3.0, the forming densityis equivalent to an operating wavelength of an infrared device of awavelength of about 1 μm. Thus, it becomes possible to set an averageforming interval of quantum dots to a scale substantially equal to thetypical structure scale d of a target texture structure. It is possibleto control an average forming interval of quantum dots according to anoperating wavelength of an optical device. Further, since quantum dotsformed as described above have a characteristic such that the quantumdots are distributed at random on a wafer surface, it is possible toeasily acquire randomly distributed quantum dots without performing aspecial process.

Thereafter, GaAs of about several μm in thickness is grown as the thirdsemiconductor layer 14 on the second semiconductor layer 13 (FIG. 5(c)).The third semiconductor layer 14 is formed in such a way that a randomconcave and convex surface of the second semiconductor layer 13 isembedded. Thereafter, the semiconductor active layer 15 made of a lightabsorbing medium including an InAs quantum dot absorbing layer is grownon the third semiconductor layer 14 (FIG. 5(d)). Specifically, after aGaAs layer is grown by about several μm by radiating Ga at a substratetemperature of 580° C. in an As atmosphere, an InAs quantum dot layer isgrown by supplying In by an amount equivalent to 2 to 3 ML at a supplyrate of 0.2 ML/s at a substrate temperature of 480° C. Unlike the caseof the second semiconductor layer 13, since a supply amount of In islarge, it is possible to form InAs quantum dots at a high density ofabout 5×10¹⁰ cm⁻². The quantum dots function as a light absorbingmedium. By growing the three-dimensional island structures by embeddingGaAs of about 50 nm in thickness, a semiconductor layer made of a lightabsorbing medium including an InAs quantum dot absorbing layer isformed. By repeating this process a plurality of times, thesemiconductor active layer 15 including a large number of InAs quantumdot layers may be manufactured. Further, the semiconductor cover layer16 made of GaAs of about several μm in thickness is successively grown,and a wafer for a semiconductor optical image sensor as illustrated inFIG. 5(e) is acquired.

Next, a process of forming a random texture structure on the thirdsemiconductor layer 14 by using the wafer is described. First, the waferis put upside down in such a way that the semiconductor substrate 11becomes an upper surface. In the semiconductor optical device in FIG. 4,signal light is incident from the upper surface. In the present exampleembodiment, a hole structure (barus structure) in which a semiconductorsubstrate on a semiconductor substrate side associated with a regionperforming light emission/light reception is removed is manufactured,and a texture structure is manufactured on a bottom portion of the hole.This is for preventing attenuation of signal light by a semiconductorsubstrate, and strengthening interaction between a texture structure anda light active layer.

In the following, a method for partially removing the semiconductorsubstrate 11 is described. First, a photoresist is coated on an undersurface of the semiconductor substrate 11 by an ordinaryphotolithography method, and an opening resist pattern 17 having apredetermined size depending on a device size is formed by contactexposure (FIG. 5(f)).

The semiconductor substrate 11 is partially removed by using the openingresist pattern 17. Specifically, an opening slightly larger than a lightreceiving surface is manufactured on a back surface of the semiconductorsubstrate 11 made of GaAs by a photolithography method, GaAs in theopening region is removed by chemical etching, and an opening structure18 is manufactured (FIG. 6(a)). In the present example embodiment, sincethe semiconductor substrate 11 is made of GaAs, it is preferable to usea mixed solution of ammonia and hydrogen peroxide water. In an actualprocess, a thin Al_(x)Ga_(1-x)As layer of about 10 nm may be insertedbetween the semiconductor substrate 11 and the first semiconductor layer12. Since a mixed solution of ammonia and hydrogen peroxide water has aproperty such that the mixed solution etches GaAs, but hardly etchesAl_(x)Ga_(1-x)As etching of the GaAs layer of the semiconductorsubstrate 11 stops at the thin Al_(x)Ga_(1-x)As layer. It is possible toselectively remove the Al_(x)Ga_(1-x)As layer exposed from the openingportion by etching using dilute hydrochloric acid, and it is easy toremove the Al_(x)Ga_(1-x)As layer without invading the GaAs layer.Consequently, it is possible to manufacture the opening structure 18 asillustrated in FIG. 6(a).

Removal of the semiconductor substrate 11 may be performed by dryetching. Further, as far as materials of the semiconductor substrate 11and the first semiconductor layer 12 are different, it is possible toperform selective etching by using a difference in etching speed betweenthe materials. Depending on a material constituting each of the layers,in a case where wet etching is performed, an etchant may be changed, andin a case where dry etching is performed, reactant gas may be changed,as necessary. In the case of the present example embodiment, since bothof the semiconductor substrate 11 and the first semiconductor layer 12are made of GaAs, which is a same substance, an etching amount may becontrolled by an etching rate and an etching time, and etching may beperformed up to a boundary between the semiconductor substrate 11 andthe first semiconductor layer 12.

After the partial removal of the semiconductor substrate 11 is finished,the first semiconductor layer 12 is removed by selective etching,etching is proceeded up to an interface of the second semiconductorlayer 13, and the second semiconductor layer 13 is exposed within theopening structure 18. In the case of the present example embodiment,since the first semiconductor layer 12 is made of GaAs, and the secondsemiconductor layer 13 is made of In_(x)Ga_(1-x)As or InAs, it ispreferable to employ dry etching by chlorine gas for the firstsemiconductor layer 12. Dry etching by chlorine gas is able to etchGaAs. However, in a case where a material containing In is used, anetching speed of the material drastically decreases, and the material ishardly etched. Therefore, in dry etching by chlorine gas, the etchingstops at an interface with respect to the second semiconductor layer 13containing In (FIG. 6(b)). The etching method is not limited to thepresent method, as far as there is etching selectivity between a firstsemiconductor layer and a second semiconductor layer.

Subsequently, etching is proceeded up to a surface of the thirdsemiconductor layer 14 by removing the second semiconductor layer 13exposed within the opening structure 18 by selective etching (FIG.6(c)). In this case, since the second semiconductor layer 13 is made ofIn_(x)Ga_(1-x)As or InAs, and the third semiconductor layer 14 is madeof GaAs, it is preferable to use hydrochloric acid as an etchant. In acase where this method is employed, conversely to dry etching bychlorine gas, In_(x)Ga_(1-x)As or InAs is etched, but GaAs is hardlyetched. As a result of the process, a hole structure 19 associated witha shape of a nanostructure included in the second semiconductor layer 13as illustrated in FIG. 6(c) appears on a surface of the thirdsemiconductor layer 14. A surface configuration of the hole structure 19is associated with a two-dimensional distribution of nanostructures ofthe second semiconductor layer 13, a forming position is random, and anaverage forming interval of holes becomes a value substantially equal tothe typical structure scale d.

When a depth of a hole of the hole structure 19 is sufficient forexhibiting a characteristic of a random texture structure, the holestructure 19 may be employed as a texture structure. When a depth of ahole of the hole structure 19 is not sufficient to be employed as atexture structure, etching may be further proceeded in such a way that adeep hole is formed by using these holes as a seed, and a random texturestructure 20 may be formed (FIG. 6(d)). The etchant is not specificallylimited, as far as a forming interval of holes can be secured. However,an etchant that selectively etches a defect or the like being present ona surface is more preferable. For example, it is possible to use, as anetchant, a mixed solution of hydrochloric acid, acetic acid, andhydrogen peroxide water. A mixing ratio of a mixed solution ofhydrochloric acid, acetic acid, and hydrogen peroxide water may be suchthat hydrochloric acid:acetic acid:hydrogen peroxide water=1:2:1, forexample. By performing etching by a mixed solution as described above, ahole (defect) portion is etched deeper, and it is possible tomanufacture the random texture structure 20 having a large distributionalso in a depth direction. A semiconductor optical device having arandom texture structure within a barus structure illustrated in FIG. 4is completed by removing the opening resist pattern 17 after the randomtexture structure 20 is manufactured.

FIG. 9 illustrates a surface photograph of one example of a randomtexture structure to be manufactured on GaAs. A portion where a defect(hole) is present on a surface is selectively etched, and a structure(random texture structure) having a random concave and convex is formed.

(Description on Advantageous Effects)

In the present example embodiment, it is possible to manufacture, in asimplified way, the hole structure 19 and the random texture structure20 in which a size and a forming interval are controlled on a surface ofthe third semiconductor layer 14. Further, in the present exampleembodiment, it is possible to manufacture, in a simplified way, the holestructure 19 and the random texture structure 20 in which a size and aforming interval are controlled on a bottom surface inside a holestructure (barus structure) in which the semiconductor substrate 11 ispartially removed.

Since a barus structure has a large concave and convex on a surfacebecause a substrate is etched into a hole shape, it is extremelydifficult to manufacture a texture structure by an ordinaryphotolithography method. Contrary to this, in the texture structuremanufacturing method according to the present example embodiment, thesecond semiconductor layer 13 is grown by a crystal growth method. Athree-dimensional island (quantum dot) of a nanostructure is formed at arandom position on a growing surface by using a self-forming phenomenonof a crystal growth process, and the hole structure 19 and the randomtexture structure 20 are manufactured by using the above.

Thus, in the texture structure manufacturing method according to thepresent example embodiment, it is possible to manufacture the randomtexture structure 20, while omitting manufacturing a mask for a randompattern. Further, in the texture structure manufacturing methodaccording to the present example embodiment, a structure of an etchingpattern for manufacturing a texture structure is embedded by crystalgrowth at a stage of manufacturing a wafer beforehand. Therefore, evenafter a hole structure is manufactured, it is possible to manufacture atexture structure only by etching. Further, regarding the pattern by ananostructure that is manufactured beforehand, it is possible to controla density, a size, a shape, and a structure of a nanostructure bychanging a growing condition of crystal growth. Thus, it is possible todesign a desired pattern according to a semiconductor light element tobe manufactured.

Note that a random texture structure may also be formed on a surface(semiconductor cover layer 16) on the opposite side as necessary. Inthis case, the method according to the present example embodiment may beemployed, or an ordinary photolithography method may be employed.Further, in the present example embodiment, InAs is used as a materialfor a quantum dot, and GaAs is used as a material for embedding thequantum dot. The material, however, is not limited to the above. As thequantum dot materials/embedding materials other than the above, forexample, there are In_(x)Ga_(1-x)As/GaAs,In_(x)Al_(1-x)As/Al_(x)Ga_(1-x)As or GaAs,InP/InP/Ga_(x)In_(1-x)As_(y)P_(1-y), and the like. The present exampleembodiment can be achieved by employing an etching method according toeach of the material groups.

Second Example Embodiment

Next, a texture structure manufacturing method according to a secondexample embodiment of the present invention is described. The firstexample embodiment describes a method for manufacturing the randomtexture structure 20 on a bottom of a hole structure (barus structure)in which the semiconductor substrate 11 is partially removed. In a casewhere a total of thicknesses of growing layers from the thirdsemiconductor layer 14 to the semiconductor cover layer 16 in the firstexample embodiment is sufficiently large, and the growing layers can bemaintained even when a substrate is removed over the entire surface, ora case where a growing layer is joined to another semiconductorsubstrate or the like, it is also possible to manufacture a randomtexture structure by using a photolithography method by manufacturing amask for a random pattern according to a background art. However, in themethod according to the present example embodiment, it is possible tomanufacture a random texture structure in a more simplified way.Elements similar to those in the first example embodiment are indicatedwith same reference numbers, and detailed description thereof isomitted.

(Description on Configuration)

FIG. 10 is a cross-sectional view of a semiconductor optical device tobe manufactured by a texture structure manufacturing method according tothe second example embodiment of the present invention. FIGS. 11(a) to11(d), and 12(a) to 12(d) are cross-sectional views illustrating amanufacturing process of the semiconductor optical device in FIG. 10.

The semiconductor optical device in FIG. 10 includes a thirdsemiconductor layer 14, a semiconductor active layer 15, and asemiconductor cover layer 16. A random texture structure 20 is formed onthe third semiconductor layer 14. The semiconductor optical device inFIG. 10 is a device in a case where a semiconductor substrate is removedover the entire surface.

(Description on Manufacturing Method)

Referring to FIGS. 11 and 12, the texture structure manufacturing methodaccording to the present example embodiment is described. FIGS. 11 and12 illustrate a random texture structure manufacturing process in whicha semiconductor substrate 11 is finally removed over the entire surface.First, similarly to the first example embodiment, each of layersincluding a semiconductor active layer is grown by a crystal growthmethod. Specifically, a first semiconductor layer 12 made of GaAs isgrown on one major surface of the semiconductor substrate 11 (FIG.11(a)). Next, as one example of a layer having concaves and convexes onwhich nanostructures are randomly distributed, a second semiconductorlayer 13 is grown (FIG. 11(b)). Next, the third semiconductor layer 14is grown on the second semiconductor layer 13 (FIG. 11(c)). Next, thesemiconductor active layer 15 is grown on the third semiconductor layer14, and then, the semiconductor cover layer 16 is grown (FIG. 11(d)). Aprocess being a wafer manufacturing process until the semiconductorcover layer 16 is grown is similar to the first example embodiment.

Next, a process of forming a random texture structure on the thirdsemiconductor layer 14 by using the wafer is described. First, the waferis put upside down in such a way that the semiconductor substrate 11becomes an upper surface (FIG. 12(a)). Next, the semiconductor substrate11 is removed over the entire surface. The removal of the semiconductorsubstrate 11 is performed by wet etching or dry etching. When materialsof the semiconductor substrate 11 and the first semiconductor layer 12are different, it is possible to perform selective etching by using adifference in etching speed between the materials. Depending on amaterial constituting each of the layers, in a case where wet etching isperformed, an etchant may be changed, and in a case where dry etching isperformed, reactant gas may be changed, as necessary. Further, similarlyto the first example embodiment, an etch stop layer may be introduced.In the case of the present example embodiment, since both of thesemiconductor substrate 11 and the first semiconductor layer 12 are madeof GaAs, which is a same substance, an etching amount is controlled byan etching rate and time, and etching is performed up to a boundarybetween the semiconductor substrate 11 and the first semiconductor layer12 (FIG. 12(b)).

After the removal of the semiconductor substrate 11 is finished, thefirst semiconductor layer 12 is removed by selective etching, and asurface of the second semiconductor layer 13 is exposed. In the case ofthe present example embodiment, since the first semiconductor layer 12is made of GaAs, and the second semiconductor layer 13 is made ofIn_(x)Ga_(1-x)As or InAs, similarly to the first example embodiment, itis preferable to employ dry etching by chlorine gas for removal of thefirst semiconductor layer 12 made of GaAs. By the above-describedprocess, it is possible to acquire a structure in which the secondsemiconductor layer 13 is exposed on a surface (FIG. 12(c)).

Subsequently, etching is proceeded up to a surface of the thirdsemiconductor layer 14 by removing the second semiconductor layer 13 byselective etching. In this case, since the second semiconductor layer 13is made of In_(x)Ga_(1-x)As or InAs, and the third semiconductor layer14 is made of GaAs, wet etching by hydrochloric acid as an etchant isemployed. As a result of the etching, a hole structure 19 associatedwith a nanostructure included in the second semiconductor layer 13 asillustrated in FIG. 12(d) appears on a surface of the thirdsemiconductor layer 14.

When a depth of a hole is sufficient for exhibiting a characteristic ofa random texture structure, since the hole structure 19 can be employedas a random texture structure, the manufacturing process is finished.Specifically, the manufacturing process may be finished not for thesemiconductor optical device illustrated in FIG. 10 but for asemiconductor optical device having the hole structure 19 illustrated inFIG. 12(d).

When a depth of a hole is not sufficient, similarly to the first exampleembodiment, etching is further proceeded in such a way that a deep holeis formed by using these holes as a seed. The etchant is notspecifically limited, as far as a forming interval of holes can besecured. However, an etchant that selectively etches a defect or thelike being present on a surface is more preferable. For example, byperforming etching by a mixed solution being hydrochloric acid:aceticacid:hydrogen peroxide water=1:2:1, a hole (defect) portion is etcheddeeper. Therefore, it is possible to manufacture a random texturestructure having a large distribution also in a depth direction. Aregion where a defect is present on a surface is selectively etched bythe etching, and the random texture structure 20 having a random concaveand convex is formed (FIG. 10).

The hole structure 19 and the random texture structure 20 are associatedwith a distribution of nanostructures serving as a seed. In the case ofthe present example embodiment, since a quantum dot is used as ananostructure, a forming position is random. An average forming intervalof quantum dots is controlled in such a way as to become a scalesubstantially equal to a typical structure scale d, which is intended tobe manufactured in a first quantum dot manufacturing process. Therefore,a forming position of concave and convex of a texture structure formedon a surface is random, and an average forming interval also becomes ascale substantially equal to the typical structure scale d, which isintended to be manufactured. Consequently, it is possible to acquire therandom texture structure 20.

Note that, also in a structure before the second semiconductor layer 13is removed in FIG. 12(b) or 12(c), a texture structure having a randomdistribution in which an average interval is the structure parameter dis formed on a surface. It is possible to employ a state before thesecond semiconductor layer 13 is removed in FIG. 12(b) or 12(c), as arandom texture structure, depending on a device structure or anothercondition.

(Description on Advantageous Effects)

In the present example embodiment, similarly to the first exampleembodiment, it is possible to manufacture, in a simplified way, therandom texture structure 20 in which a size and a forming interval arecontrolled on a surface of the third semiconductor layer 14. In thetexture structure manufacturing method according to the present exampleembodiment, similarly to the first example embodiment, the secondsemiconductor layer 13 is grown by a crystal growth method. Athree-dimensional island (quantum dot) of a nano structure is formed ata random position on a growing surface by using a self-formingphenomenon of a crystal growth process, and the hole structure 19 andthe random texture structure 20 are manufactured by using the above.

Thus, in the texture structure manufacturing method according to thepresent example embodiment, similarly to the first example embodiment,it is possible to manufacture the random texture structure 20, whileomitting manufacturing a mask for a random pattern.

Third Example Embodiment

Next, a texture structure manufacturing method according to a thirdexample embodiment of the present invention is described. In the firstand second example embodiments, a quantum dot is used as a nanostructure of the second semiconductor layer 13. However, a nanostructureis not limited to a quantum dot.

FIG. 13 is an atomic force microphotograph of a manufacturing example ofa nanostructure having a structure in which several quantum dots areaggregated. FIG. 13 illustrates a state that some of isolated quantumdots illustrated in FIG. 8 are combined into an aggregate, and a newnanostructure is formed. The three-dimensional structures are such thatnot only a forming position thereof is random similarly to the firstexample embodiment, but also the number of combined quantum dots israndom. Therefore, a size (height) of an aggregate also becomes random.

FIG. 14 is an electron microphotograph of a manufacturing example of ananostructure formed by combining a large number of quantum dots. FIG.14 is an electron microphotograph of a nanostructure to be formed, whena supply amount of InAs, which is 2 ML or less when a nanostructure inthe first example embodiment is manufactured, is further increased, and

InAs of about 100 ML is supplied. A structure of a size of about several100 nm is formed on a surface over the entire surface. The surface ofthe nanostructures is surrounded by a certain specific crystal plane,and a shape thereof is also random. In the third example embodiment, acase that the structures are used as a nanostructure included in asecond semiconductor layer is described.

(Description on Configuration)

A semiconductor optical device in FIG. 15 includes a third semiconductorlayer 14, a semiconductor active layer 15, and a semiconductor coverlayer 16. A random texture structure 20 is formed on the thirdsemiconductor layer 14. Similarly to the second example embodiment, thesemiconductor optical device in FIG. 15 is a device in a case where asemiconductor substrate is removed over the entire surface.

(Description on Manufacturing Method)

In the following, a method for manufacturing the semiconductor opticaldevice in FIG. 15 is described. FIGS. 16(a) to 16(d), and 17(a) to 17(d)are cross-sectional views illustrating a manufacturing process of thesemiconductor optical device in FIG. 15. FIGS. 16 and 17 illustrate aprocess of manufacturing a random texture structure by using athree-dimensional structure in which a nanostructure included in asecond semiconductor layer is not a quantum dot. Note that the processin the present example embodiment is similar to the second exampleembodiment, except for a nanostructure manufacturing process.

First, a semiconductor substrate 11 made of GaAs is prepared, and afirst semiconductor layer 12 made of GaAs is grown on one major surfaceof the semiconductor substrate 11 in accordance with a procedure similarto the first and second example embodiments (FIG. 16(a)). Next, as oneexample of a layer including a concave and convex surface on whichnanostructures are randomly distributed, a second semiconductor layer 13is grown (FIG. 16(b)). The present example embodiment describes anexample in which a three-dimensional structure illustrated in FIG. 14 isused as a nanostructure. After a GaAs layer is grown by about several μmby radiating Ga at a substrate temperature of 580° C. in an Asatmosphere, a three-dimensional structure formed by combining a largenumber of InAs quantum dots is formed by supplying In by an amountequivalent to about 100 ML. In the three-dimensional structure, sincedistortion due to lattice inconsistency in constituent substance betweena substrate being grown and a growing layer is formed, it is necessaryto reduce an influence of occurrence of transposition accompanied by thedistortion. In the present example embodiment, the third semiconductorlayer 14 made of GaAs is grown by several μm (herein, 3 μm) on thesecond semiconductor layer 13 (FIG. 16(c)). By the growth of the thirdsemiconductor layer 14, it is possible to avoid an influence bydistortion.

Processes thereafter are similar to those of the second exampleembodiment. The semiconductor active layer 15 is grown on the thirdsemiconductor layer 14, and the semiconductor cover layer 16 is grown(FIG. 16(d)). Next, the wafer is put upside down in such a way that thesemiconductor substrate 11 becomes an upper surface (FIG. 17(a)). Next,the semiconductor substrate 11 is removed over the entire surface. Inthe case of the present example embodiment, since both of thesemiconductor substrate 11 and the first semiconductor layer 12 are madeof GaAs, which is a same substance, an etching amount is controlled byan etching rate and time, and etching is performed up to a boundarybetween the semiconductor substrate 11 and the first semiconductor layer12 (FIG. 17(b)). After the removal of the semiconductor substrate 11 isfinished, the first semiconductor layer 12 is removed by selectiveetching, and a surface of the second semiconductor layer 13 is exposed.In the case of the present example embodiment, since the firstsemiconductor layer 12 is made of GaAs, and the second semiconductorlayer 13 is made of In_(x)Ga_(1-x)As or InAs, similarly to the firstexample embodiment, it is preferable to employ dry etching by chlorinegas for removal of the first semiconductor layer 12 made of GaAs. As aresult, a structure in which the second semiconductor layer 13 made ofIn_(x)Ga_(1-x)As or InAs is exposed on a surface is acquired (FIG.17(c)). Subsequently, etching is proceeded up to a surface of the thirdsemiconductor layer 14 by removing the second semiconductor layer 13 byselective etching. In this case, since the second semiconductor layer 13is made of In_(x)Ga_(1-x)As or InAs, and the third semiconductor layer14 is made of GaAs, it is preferable to employ wet etching byhydrochloric acid as an etchant. As a result of the etching, a holestructure 19 associated with a nanostructure included in the secondsemiconductor layer 13 as illustrated in FIG. 17(d) appears on a surfaceof the third semiconductor layer 14.

When a depth of a hole of the hole structure 19 is sufficient forexhibiting a characteristic as a texture structure, the hole structure19 is employed as a texture structure. Then, the texture structuremanufacturing process is finished. Specifically, the manufacturingprocess may be finished not for the semiconductor optical deviceillustrated in FIG. 15 but for a semiconductor optical device having thehole structure 19 illustrated in FIG. 17(d).

Similarly to the first and second example embodiments, when a depth of ahole of the hole structure 19 is not sufficient, etching is furtherproceeded by using the holes as a seed, and the random texture structure20 is formed. The etchant is not specifically limited, as far as aforming interval of holes can be secured. However, an etchant thatselectively etches a defect or the like being present on a surface ismore preferable. For example, by performing etching by a mixed solutionbeing hydrochloric acid:acetic acid:hydrogen peroxide water=1:2:1, ahole (defect) portion is etched deeper. Therefore, it is possible tomanufacture a random texture structure having a large distribution alsoin a depth direction. A region where a defect is present on a surface isselectively etched by the etching, and the random texture structure 20is formed (FIG. 15).

The hole structure 19 and the random texture structure 20 formed on asurface are associated with a distribution of nanostructures serving asa seed. In the case of the present example embodiment, since athree-dimensional structure formed by combining a large number of InAsquantum dots is employed as a nanostructure, a forming position israndom, and an average forming interval of quantum dots is controlled insuch a way as to become a scale substantially equal to a typicalstructure scale d, which is intended to be manufactured in a firstquantum dot manufacturing process. Therefore, a forming position ofconcave and convex of a texture structure formed on a surface is random,and an average forming interval also becomes a scale substantially equalto the typical structure scale d, which is intended to be manufactured.Consequently, it is possible to acquire the random texture structure 20.

Note that also in a structure before the second semiconductor layer 13is removed in FIG. 17(b) or 17(c), the random texture structure 20having a random distribution in which an average interval is thestructure parameter d is formed on a surface. It is possible to employ astate before the second semiconductor layer 13 is removed in FIG. 17(b)or 17(c), as a random texture structure, depending on a device structureor another condition.

(Description on Advantageous Effects)

In the present example embodiment, similarly to the first and secondexample embodiments, it is possible to manufacture, in a simplified way,the random texture structure 20 in which a size and a forming intervalare controlled on a surface of the third semiconductor layer 14. In thetexture structure manufacturing method according to the present exampleembodiment, the second semiconductor layer 13 is grown by a crystalgrowth method. A three-dimensional island (quantum dot) of ananostructure is formed at a random position on a growing surface byusing a self-forming phenomenon of a crystal growth process, and thehole structure 19 and the random texture structure 20 are manufacturedby using the above.

Thus, in the texture structure manufacturing method according to thepresent example embodiment, similarly to the first and second exampleembodiments, it is possible to manufacture the random texture structure20, while omitting manufacturing a mask for a random pattern.

Further, in the present example embodiment, as a nanostructure of thesecond semiconductor layer 13, not a quantum dot as described in thefirst and second example embodiments, but a three-dimensional structurehaving a structure in which several quantum dots are aggregated isemployed. In a three-dimensional structure as described in the presentexample embodiment, similarly to the first and second exampleembodiments, not only that a forming position of the three-dimensionalstructure is at random, but also that the number of combined quantumdots is random. Therefore, a size (height) of an aggregate also becomesrandom.

All of the nanostructures included in the second semiconductor layer 13described in the first, second and third example embodiments aremanufactured by using a self-forming phenomenon in a crystal growthprocess. In other words, unlike a method such as photolithography, it ispossible to manufacture a nanostructure only by supplying a specific rawmaterial in a crystal growing device, without the need of a mask or thelike, for forming a structure, such as a resist or a dielectric.Therefore, the present method is very simple, and is less likely to beaffected by contamination accompanied by a process. Further, a formingposition is basically random, and it is possible to control an averageinterval of concaves and convexes of the structure by changing a basicgrowing condition of crystal growth such as a growth speed and a growthtemperature. It is possible to arbitrarily design according to aspecification of a device.

Fourth Example Embodiment

Next, a texture structure manufacturing method according to a fourthexample embodiment of the present invention is described. The presentexample embodiment is one example of a case where the above-describedtexture manufacturing method is applied to a more specific thin filmsemiconductor optical sensor manufacturing method or random texturestructure manufacturing process.

FIG. 18 is a cross-sectional view of a thin film semiconductor opticalsensor according to the fourth example embodiment to be manufactured byapplying a texture structure manufacturing method according to anexample embodiment of the present invention. FIGS. 19(a) to 19(d), and20(a) to 20(d) are cross-sectional views illustrating a thin filmsemiconductor optical sensor manufacturing process according to thefourth example embodiment.

(Description on Configuration)

The thin film semiconductor optical sensor in FIG. 18 is a lightreceiving image sensor 100. The light receiving image sensor 100 in FIG.18 includes a light absorbing medium 103, a second electrode 107, afirst electrode 108, a first n-doped layer 109, a passivation film 111,a metal bump 112, a readout circuit chip 113, thermoset resin 114, and arandom texture structure 115.

Herein, regarding an example of an infrared light receiving elementemploying an InAs quantum dot absorbing layer formed in a GaAssemiconductor layer, as the light absorbing medium 103 being asemiconductor active layer, one example of a manufacturing processincluding integrating into a readout circuit is described. The presentmanufacturing process described here is merely one example of amanufacturing process of a main constituent element of the present thinfilm semiconductor optical sensor element. An actual thin filmsemiconductor optical sensor element may be modified, as far as themodification exhibits an advantageous effect described in the presentexample embodiment by a component factor of another device structure.

(Description on Manufacturing Method)

A manufacturing method is described by using FIG. 19. First, a GaAssubstrate 102 is prepared, and introduced into a growing device. In thepresent process, a molecular beam epitaxy device is employed as oneexample of the growing device. As far as the growing device is able tomanufacture a thin film structure, another device, for example, anorganic metal thermally decomposable film forming device may beavailable. A natural oxide film on a substrate surface is removed by anordinary substrate surface cleaning treatment such as raising asubstrate temperature up to about 600° C., while radiating As.Thereafter, a nanostructure layer 105 containing In_(x)Ga_(1-x)As isgrown according to a method similar to the third example embodiment. Anaverage forming interval of structures of the nanostructure layer 105 isassumed to be a scale substantially equal to a typical structure scaled, which is intended to be manufactured.

Thereafter, a GaAs layer is formed in such a way that a random patternof a structure of the nanostructure layer 105 is embedded, and a secondn-doped layer 110 is grown. The second n-doped layer 110 is formed inorder to secure an ohmic contact with the first electrode 108 to beformed later. Thereafter, the light absorbing medium 103 including anInAs quantum dot absorbing layer is grown. Specifically, after a GaAslayer is grown by about several μm by radiating Ga at 580° C. in an Asatmosphere, an InAs quantum dot layer is grown by supplying In by anamount equivalent to 2 to 3 ML at a substrate temperature of 480° C. Bygrowing a three-dimensional island structure composed of the InAsquantum dot layers by embedding GaAs of about 50 nm in thickness, thelight absorbing medium 103 including an InAs quantum dot absorbing layeris formed. By repeating this process a plurality of times, a quantum dotabsorbing layer composed of a large number of InAs quantum dots may bemanufactured. Further, after GaAs of about several μm in thickness issuccessively grown again, the growth of the light absorbing medium 103is finished. Further, by growing the first n-doped layer 109 on thelight absorbing medium 103, a wafer for a thin film semiconductoroptical image sensor as illustrated in FIG. 19(a) is acquired. The firstn-doped layer 109 is formed in order to secure an ohmic contact with thesecond electrode 107 to be formed later.

Next, in order to separate the light absorbing medium 103 into eachelement, a mesa structure 106 is formed by anisotropic etching (e.g., amixed solution of ammonia water and hydrogen peroxide water) (FIG.19(b)). The second electrode 107 and the first electrode 108 arerespectively formed by vapor deposition on the first n-doped layer 109on each of the mesa structures 106, and on the second n-doped layer 110that appears by etching (FIG. 19(c)). Further, the passivation film 111(e.g. SiO₂) is formed in such a way that an opening is located on anelectrode portion by the second electrode 107 and the first electrode108 (FIG. 19(d)).

Furthermore, a metal bump 112 (e.g. an indium bump) is formed on thesecond electrode 107 and the first electrode 108 in an opening of thepassivation film 111 (FIG. 20(a)). Lastly, a wafer is cut into each chipto form a light receiving chip.

Next, the readout circuit chip 113 in which a signal readout circuit isintegrated in association with a cut light receiving chip is prepared,and the flipped light receiving chip and the readout circuit chip 113are bonded with flip chip manner (FIG. 20(b)). For the purpose ofincreasing a mechanical strength of a device, the thermoset resin 114 isfilled in a clearance between the light receiving chip and the readoutcircuit chip 113 (FIG. 20(c)).

Next, the GaAs substrate 102 of the light receiving chip is removed byselective wet etching (e.g. a mixture of citric acid and hydrogenperoxide water), and the nanostructure layer 105 is exposed (FIG.20(d)). Further, by removing the nanostructure layer 105 by selectivewet etching with GaAs (e.g. buffered hydrofluoric acid), a GaAs layer116 having a quantum dot random pattern embedded therein is exposed, andthe light receiving image sensor 100 in which the random texturestructure 115 having a structure such that a shape of quantum dots ofthe nanostructure layer 105 is transferred in the vicinity of a lightreceiving layer is formed is completed (FIG. 18).

(Description on Advantageous Effects)

In the present example embodiment, it is possible to manufacture, in asimplified way, the random texture structure 115 in which a size and aforming interval are controlled in the light receiving image sensor 100.In the manufacturing method of the random texture structure 115according to the present example embodiment, similarly to the first tothird example embodiments, the nanostructure layer 105 is grown by acrystal growth method. A three-dimensional island (quantum dot) of ananostructure is formed at a random position on a growing surface byusing a self-forming phenomenon of a crystal growth process, and therandom texture structure 115 is manufactured by using the above.

Thus, it is possible to manufacture the random texture structure 115,while omitting manufacturing a mask for a random pattern. Further, it ispossible to manufacture the light receiving image sensor 100 having therandom texture structure 115 by applying a manufacturing process of athin film semiconductor optical sensor.

Further, in the present example embodiment, it is possible tomanufacture the random texture structure 115 at a position very close tothe light absorbing medium 103 including an InAs quantum dot absorbinglayer. Thus, it is possible to manufacture the light receiving imagesensor 100 having the random texture structure 115 capable of reducingcrosstalk by scattered light.

In the present example embodiment, it is possible to manufacture thelight receiving image sensor 100 in which a texture structure having arandom planar orientation is formed on a light receiving surface.Therefore, it is possible to improve reliability, and reduce a problemon productivity. In the present example embodiment, it is possible toprovide a thin film semiconductor optical sensor capable of sufficientlyexhibiting potential performance thereof.

Fifth Example Embodiment

Next, a texture structure manufacturing method according to a fifthexample embodiment of the present invention is described. Similarly tothe fourth example embodiment, the present example embodiment is oneexample of a case where the above-described texture structuremanufacturing method is applied to a more specific thin filmsemiconductor optical sensor manufacturing method or random texturestructure manufacturing process.

FIG. 21 is a cross-sectional view of a thin film semiconductor opticalsensor to be manufactured by applying a texture structure manufacturingmethod according to the fifth example embodiment of the presentinvention. FIGS. 22(a) to 22(d), 23(a) to 23(c), and 24(a) and 24(b) arecross-sectional views illustrating a manufacturing process of the thinfilm semiconductor optical sensor in FIG. 21.

(Description on Configuration)

The thin film semiconductor optical sensor in FIG. 21 is a lightreceiving image sensor 200. Similarly to the fourth example embodiment,the light receiving image sensor 200 in FIG. 21 includes a lightabsorbing medium 103, a second electrode 107, a first electrode 108, afirst n-doped layer 109, a passivation film 111, a metal bump 112, areadout circuit chip 113, and a thermoset resin 114. Further, the lightreceiving image sensor 200 in FIG. 21 includes a random texturestructure 215.

(Description on Manufacturing Method)

The light receiving image sensor 200 in the present example embodimentis manufactured by a manufacturing process similar to the fourth exampleembodiment up to FIGS. 22(a) to 22(d), 23(a) to 23(c), and 24(a).

Specifically, a quantum dot nanostructure layer 205 made ofIn_(x)Ga_(1-x)As is grown on a GaAs substrate 102. Herein, thenanostructure layer 205 in the present example embodiment is assumed tohave a dot growth density of a scale substantially equal to a typicalstructure scale d of a scattering surface, which is intended to bemanufactured.

Thereafter, a GaAs layer is formed in such a way that a random patternof a structure of the nanostructure layer 205 is embedded, and a secondn-doped layer 110 is grown. The second n-doped layer 110 is formed inorder to secure an ohmic contact with the first electrode 108 to beformed later. Thereafter, the light absorbing medium 103 including anInAs quantum dot absorbing layer is grown. Further, by growing the firstn-doped layer 109 on the light absorbing medium 103, a wafer for a thinfilm semiconductor optical image sensor as illustrated in FIG. 22(a) isacquired. The first n-doped layer 109 is formed in order to secure anohmic contact with the second electrode 107 to be formed later.

Next, in order to separate the light absorbing medium 103 into eachelement, a mesa structure 106 is formed by anisotropic etching (FIG.22(b)). The second electrode 107 and the first electrode 108 arerespectively formed by vapor deposition on the first n-doped layer 109on each of the mesa structures 106, and on the second n-doped layer 110that appears by etching (FIG. 22(c)). Further, the passivation film 111is formed in such a way that an opening is located on an electrodeportion by the second electrode 107 and the first electrode 108 (FIG.22(d)). Furthermore, the metal bump 112 is formed on the secondelectrode 107 and the first electrode 108 in an opening of thepassivation film 111 (FIG. 23(a)). Lastly, a wafer is cut into each chipto form a light receiving chip. Next, the readout circuit chip 113 inwhich a signal readout circuit is integrated in association with a cutlight receiving chip is prepared, and the flipped light receiving chipand the readout circuit chip 113 are bonded with flip chip manner (FIG.23(b)). For the purpose of increasing a mechanical strength of a device,the thermoset resin 114 is filled in a clearance between the lightreceiving chip and the readout circuit chip 113 (FIG. 23(c)).

Next, a GaAs substrate of the light receiving chip is removed byselective wet etching (e.g. a mixture of citric acid and hydrogenperoxide water), and the nanostructure layer 205 is exposed (FIG.24(a)). Further, the nano structure layer 205 is removed. In the presentexample embodiment, after the nanostructure layer 205 is removed, a GaAslayer 216 in which a hole embedded with a quantum dot is formed atrandom at an interval of about a typical structure scale d is exposed(FIG. 24(b)). By performing anisotropic etching with respect to thissurface, etching is selectively proceeded in such a way that the holeembedded with a quantum dot is enlarged, and a scattering surface havingthe typical structure scale d can be acquired (FIG. 21). Thus, the lightreceiving image sensor 200 in which the random texture structure 215 isformed by using a quantum dot layer is completed.

(Description on Advantageous Effects)

In the present example embodiment, similarly to the fourth exampleembodiment, it is possible to manufacture, in a simplified way, therandom texture structure 215 in which a size and a forming interval arecontrolled in the light receiving image sensor 200. In the manufacturingmethod of the random texture structure 215 according to the presentexample embodiment, similarly to the first to fourth exampleembodiments, the nanostructure layer 205 is grown by a crystal growthmethod. A three-dimensional island (quantum dot) of a nanostructure isformed at a random position on a growing surface by using a self-formingphenomenon of a crystal growth process, and the random texture structure215 is manufactured by using the above.

Thus, it is possible to manufacture the random texture structure 215,while omitting manufacturing a mask for a random pattern. Further, it ispossible to manufacture the light receiving image sensor 200 having therandom texture structure 215 by applying a manufacturing process of athin film semiconductor optical sensor.

In the present example embodiment, it is possible to manufacture thelight receiving image sensor 100 in which a texture structure having arandom planar orientation is formed on a light receiving surface.Therefore, it is possible to improve reliability, and reduce a problemon productivity. In the present example embodiment, it is possible toprovide a thin film semiconductor optical sensor capable of sufficientlyexhibiting potential performance thereof.

In the foregoing, preferred example embodiments and examples accordingto the present invention are described. The present invention, however,is not limited to the above. For example, in the above-described exampleembodiments, a case of forming a texture on a semiconductor isdescribed. The present invention, however, is not limited to the above.A texture may be formed on a conductor or an insulator. It is possibleto control any of a density, a size, a shape, and a structure of ananostructure by changing a crystal growth condition of a nanostructure.The nanostructure may be constituted of a quantum dot, a quantum dash,or a mixed structure of either of a quantum dot structure or a quantumdash structure, or a combined structure of a quantum dot structure and aquantum dash structure. The above-described optical device may include alight emitting element or a light receiving element. Further, theabove-described optical device may be a quantum dot infrared sensor. Itis needless to say that various modifications are available within thescope of the invention described in the claims, and the modificationsare also included within the scope of the present invention.

The whole or part of the example embodiments disclosed above can bedescribed as, but not limited to, the following supplementary notes.

(Supplementary Note 1)

A method for manufacturing a texture structure comprising: growing alayer including a randomly distributed nanostructure on one majorsurface of a base material; forming a light-scattering body having thenano structure embedded therein; and exposing a surface of thelight-scattering body by removing a part or whole of the base materialand the layer including the nanostructure.

(Supplementary Note 2)

The method for manufacturing a texture structure according tosupplementary note 1, wherein an exposed surface of the light-scatteringbody has concaves and convexes.

(Supplementary Note 3)

The method for manufacturing a texture structure according tosupplementary note 1 or 2, further comprising etching a surface of thelight-scattering body by using a concave or a convex on an exposedsurface of the light-scattering body as a base point.

(Supplementary Note 4)

The method for manufacturing a texture structure according to any one ofsupplementary notes 1 to 3, further comprising controlling any of adensity, a size, a shape, and a structure of the nanostructure bychanging a crystal growth condition of a layer including thenanostructure.

(Supplementary Note 5)

The method for manufacturing a texture structure according to any one ofsupplementary notes 1 to 4, wherein the nanostructure is constituted ofa quantum dot, a quantum dash, a mixed structure of either of a quantumdot structure or a quantum dash structure, or a combined structure of aquantum dot structure and a quantum dash structure.

(Supplementary Note 6)

The method for manufacturing a texture structure according to any one ofsupplementary notes 1 to 5, wherein the light-scattering body is aconductor, a semiconductor, or an insulator.

(Supplementary Note 7)

A manufacturing method of a semiconductor optical sensor employing themethod for manufacturing a texture structure according to any one ofsupplementary notes 1 to 6, comprising: forming a semiconductor activelayer on one major surface of a semiconductor substrate; growing a layerincluding a randomly distributed nanostructure on the semiconductoractive layer; forming a light-scattering body having the nano structureembedded therein; and exposing a surface of the light-scattering body byremoving a part or whole of the base material and the layer includingthe nanostructure.

(Supplementary Note 8)

The manufacturing method of the semiconductor optical sensor accordingto supplementary note 7, further comprising: forming a barus structureby removing a part of the semiconductor substrate; and forming a texturestructure by the light-scattering body on a bottom portion of the barusstructure.

(Supplementary Note 9)

The manufacturing method of the semiconductor optical sensor accordingto supplementary note 7 or 8, further comprising forming a mesastructure of a light absorbing medium on one major surface of thelight-scattering body, after forming the light-scattering body havingthe nanostructure embedded therein.

(Supplementary Note 10)

The manufacturing method of the semiconductor optical sensor accordingto any one of supplementary notes 7 to 9, wherein the semiconductoroptical sensor includes a light emitting element or a light receivingelement.

(Supplementary Note 11)

The manufacturing method of the semiconductor optical sensor accordingto any one of supplementary notes 8 to 10, wherein the semiconductoroptical sensor is a quantum dot infrared sensor.

(Supplementary Note 12)

The manufacturing method of the semiconductor optical sensor accordingto any one of supplementary notes 8 to 11, further comprising forming amesa structure of a light absorbing medium on one major surface of thelight-scattering body, after forming the light-scattering body embeddingthe concave and convex surface.

(Supplementary Note 13)

The manufacturing method of the semiconductor optical sensor accordingto any one of supplementary notes 8 to 12, comprising: a process ofmanufacturing a semiconductor wafer including a semiconductor growinglayer having the nanostructure and the semiconductor active layer on afirst semiconductor substrate by a crystal growth method; a process ofprocessing a growing layer including the semiconductor active layer intoa mesa of a predetermined size; a process of manufacturing a bumpstructure on the mesa; a process of bonding a first semiconductorsubstrate on a second semiconductor substrate in which a signal readoutcircuit is integrated, by using the bump structure; and a process ofremoving the first semiconductor substrate and manufacturing a textureby employing the exposed nanostructure.

In the foregoing, the present invention is described by using theabove-described example embodiments as an exemplary example. The presentinvention, however, is not limited to the above-described exampleembodiments. Specifically, the present invention is applicable tovarious aspects comprehensible to a person skilled in the art within thescope of the present invention.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2017-69827 filed on Mar. 31, 2017, thedisclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

1 Optical image sensor

2 Substrate

3 Light absorbing medium

4 Light incident surface texture structure

5 Back surface texture structure

6 Light reflecting body

7 Second electrode

8 First electrode

9 Incident light

11 Semiconductor substrate

12 First semiconductor layer

13 Second semiconductor layer

14 Third semiconductor layer

15 Semiconductor active layer

16 Semiconductor cover layer

17 Opening resist pattern

18 Opening structure

19 Hole structure

20 Random texture structure

100, 200 Light receiving image sensor

102 GaAs substrate

103 Light absorbing medium

105 Nanostructure layer

106 Mesa structure

107 Second electrode

108 First electrode

109 First n-doped layer

110 Second n-doped layer

111 Passivation film

112 Metal bump

113 Readout circuit chip

114 Thermoset resin

115, 215 Random texture structure

205 Nanostructure layer

216 GaAs layer

1. A method for manufacturing a texture structure comprising: growing alayer including a randomly distributed nanostructure on one majorsurface of a base material; forming a light-scattering body having thenanostructure embedded therein; and exposing a surface of thelight-scattering body by removing a part or whole of the base materialand the layer including the nanostructure.
 2. The method formanufacturing a texture structure according to claim 1, wherein anexposed surface of the light-scattering body has concaves and convexes.3. The method for manufacturing a texture structure according to claim1, further comprising etching a surface of the light-scattering body byusing a concave or a convex on an exposed surface of thelight-scattering body as a base point.
 4. The method for manufacturing atexture structure according to claim 1, further comprising controllingany of a density, a size, a shape, and a structure of the nanostructureby changing a crystal growth condition of a layer including thenanostructure.
 5. The method for manufacturing a texture structureaccording to claim 1, wherein the nanostructure is constituted of aquantum dot, a quantum dash, a mixed structure of either of a quantumdot structure or a quantum dash structure, or a combined structure of aquantum dot structure and a quantum dash structure.
 6. The method formanufacturing a texture structure according to claim 1, wherein thelight-scattering body is a conductor, a semiconductor, or an insulator.7. A manufacturing method of a semiconductor optical sensor employingthe method for manufacturing a texture structure according to claim 1,comprising: forming a semiconductor active layer on one major surface ofa semiconductor substrate; growing a layer including a randomlydistributed nanostructure on the semiconductor active layer; forming alight-scattering body having the nanostructure embedded therein; andexposing a surface of the light-scattering body by removing a part orwhole of the base material and the layer including the nanostructure. 8.The manufacturing method of the semiconductor optical sensor accordingto claim 7, further comprising: forming a barus structure by removing apart of the semiconductor substrate; and forming a texture structure bythe light-scattering body on a bottom portion of the barus structure. 9.The manufacturing method of the semiconductor optical sensor accordingto claim 7, further comprising: forming a mesa structure of a lightabsorbing medium on one major surface of the light-scattering body,after forming the light-scattering body having the nanostructureembedded therein.
 10. The manufacturing method of the semiconductoroptical sensor according to claim 7, wherein the semiconductor opticalsensor includes a light emitting element or a light receiving element.11. The manufacturing method of the semiconductor optical sensoraccording to claim 8, wherein the semiconductor optical sensor is aquantum dot infrared sensor.
 12. The manufacturing method of thesemiconductor optical sensor according to claim 8, comprising: forming amesa structure of a light absorbing medium on one major surface of thelight-scattering body, after forming the light-scattering body embeddingthe concave and convex surface.
 13. The manufacturing method of thesemiconductor optical sensor according to claim 8, comprising: a processof manufacturing a semiconductor wafer including a semiconductor growinglayer having the nanostructure and the semiconductor active layer on afirst semiconductor substrate by a crystal growth method; a process ofprocessing a growing layer including the semiconductor active layer intoa mesa of a predetermined size; a process of manufacturing a bumpstructure on the mesa; a process of bonding a first semiconductorsubstrate on a second semiconductor substrate in which a signal readoutcircuit is integrated, by using the bump structure; and a process ofremoving the first semiconductor substrate and manufacturing a textureby employing the exposed nanostructure.